Bob,

Your point is well taken, and it is why my loop works so well even though
the match at the actual feedpoint is quite poor on some bands. The loop
itself is quite efficient and radiates what power gets to it extremely well.
I would achieve better results with an open wire feedline instead of the 50
ohm coax and ballun I am using. I may change it next year to see if I can
substantially reduce the reflected power. This was my first loop, and it was
mostly an experiment to see how well it would work. I'm extremely happy with
the loop, but not so satisfied with the way I am feeding it.  

Ron, K8HSY

-----Original Message-----
From: For blind ham radio operators [mailto:[log in to unmask]]
On Behalf Of Tom Behler
Sent: Wednesday, November 26, 2014 8:21 PM
To: [log in to unmask]
Subject: Re: SWR, antenna tuners, and reflected power

Agreed, Bob, which, in my mind, shows the complexity of all of this.

Low SWR is good, but it is not always equivalent to high efficiency.

That is why I feel that so much of this antenna stuff boils down to a real
balancing act, especially if you have limited space, a limited budget, or
both.

Tom Behler: KB8TYJ


-----Original Message-----
From: For blind ham radio operators [mailto:[log in to unmask]]
On Behalf Of Bob Tinney
Sent: Wednesday, November 26, 2014 9:16 PM
To: [log in to unmask]
Subject: Re: SWR, antenna tuners, and reflected power

I have to add something here,  I used to think that you had to have a
perfect match to maximize efficiency.  But I now realize that if you have a
good, wide range, antenna tuner, you can match almost anything.  
You can even load up an 8 foot whip on 160 meters, but the radiation
efficiency will be very low and your tuner will get very hot or arc.  I have
an Alex loop that is 3 feet in diameter and it gets out surprisingly well
even on 40 meters, but you can only use up to 20 watts do to the close
spacing in the tuning capacitor on the loop.

Bob, K8LR, [log in to unmask]

On 11/26/2014 4:24 PM, Tom Behler wrote:
> Ron:
>
> Thanks for the excellent concept review on SWR, reflected power, and 
> antenna tuners.
>
> We all need reminders about this sort of thing from time to time.
>
> In fact, I'm now thinking of making some modifications to my station, 
> and am trying to decide whether I can effectively do so with my 
> current antenna arrangement.  As you may recall, I use an Alpha Delta 
> DXCC nulti-band dipole on 40 through 10 meters, and a Cobra ultralite 
> senior antenna, mainly for the lower bands.
>
> While these antennas have kept me on the air on the HF bands over the 
> past few years, I do wonder sometimes whether I might try something 
> else to improve my situation.  I do have limited space here, though, 
> which makes the issue of alternate wire antennas a bit challenging.  A 
> tower and beam are also out of the question at this time for financial 
> and other more practical reasons.
>
>
> Anyway, your remarks are quite timely here, so thanks for sharing them.
>
> Tom Behler: KB8TYJ
>
>
> -----Original Message-----
> From: For blind ham radio operators
> [mailto:[log in to unmask]]
> On Behalf Of Dr. Ronald E. Milliman]\\`
> Sent: Wednesday, November 26, 2014 4:07 PM
> To: [log in to unmask]
> Subject: SWR, antenna tuners, and reflected power
>
> I am sure most of you know all about SWR (i.e. Standing Wave Ratio), 
> antenna tuners, and reflected power. However, it might be worth our 
> discussing it anyway for the benefit of those who might not be as 
> familiar with these relationships as others. Many of us use antenna 
> tuners, both manual and automatic, for obtaining the best possible 
> impedance match at the output point of our transceivers with the 
> objective of getting the SWR as close to
> 1.0 to 1 as we can. A perfect match for most rigs is when the 
> transceiver sees a 50 ohm load at its output. Anything above a 1:1 SWR 
> represents some level of mismatch. Most of our transceivers can 
> tolerate some mismatch before it begins to reduce the power output as 
> a means of protecting the circuitry of the transceiver, and if the SWR 
> or mismatch gets high enough, it will cause the transceiver to reduce 
> its power output to zero. Many of us have transceivers, like the 
> Kenwood TS-590 and similar rigs, that have built-in automatic antenna 
> tuners. These tuners work extremely well for matching the impedance 
> presented to the transceiver at its output, providing this mismatch 
> isn't too high. How much is too high varies to some extent from one 
> make and model of transceiver to another. If the mismatch is so large 
> that the rigs internal automatic tuner cannot bring the SWR down 
> within an acceptable level, you are faced with either adjusting your 
> antenna to achieve a better match at the point where the feedline 
> connects
to the antenna, or you will need to obtain an external tuner to do the job.
> External tuners, whether manual or automatic, tend to have much wider 
> ranges for matching the impedance of the feedline to the 50 ohms the 
> transceiver wants to see at its output. A match at the transceiver's 
> output does not mean there is a match at the point where the feedline 
> actually connects to the antenna. Even if the impedance at the output 
> of the transceiver is matched perfectly with an antenna tuner, there 
> can be a very substantial mismatch at the other end of the feedline 
> where
it connects to the antenna.
> The larger this latter mismatch, the less actual power will be 
> radiated by the antenna and the more power from the transceiver will 
> be reflected back or remain in the feedline. What happens to the 
> reflected power depends largely on the type of feedline used. The 
> difference between the power radiated by the antenna and the output 
> power of the transceiver is the reflected power and may be totally 
> lost power, depending upon the loss rating of the feedline. If coax is 
> used for the feedline, this reflected power ends up dissipating as 
> heat in the coax and is pretty much totally lost power. If this heat 
> is more than the coax can handle, it can burn up the coax. In 
> contrast, open wire feedline is considerably less "lossy", and much of 
> the reflected power ends up being radiated by the open wire feedline 
> as
opposed to ending up being dissipated in heat.
>
>   
>
> I am building up to two very important points that, in my opinion, do 
> not received nearly as much attention as they should. The first point 
> is that reflected power is not good for your transceiver, or if you 
> are using a linear amplifier, it is not good for your amp. If you are 
> using a tube-type linear, it can handle or tolerate more reflected 
> power than the solid-state type amps, but regardless, reflected power 
> is
bad for your rig and it is bad
> for your amp. Here is    my second point: just because your antenna tuner
is
> able to get the SWR down to 1.0 to 1 or an acceptable level at the 
> output of your transceiver or amp, that does not mean the reflected 
> power is zero or reduced to an acceptable level. Most rigs and amps 
> today have built-in protection circuits that detect high SWR and high 
> reflected power, and they will shut completely down if either the SWR 
> or
reflected power is too high.
> For example, I have a Kenwood TS-590 driving an Ameritron ALS-600, and 
> my antenna is an 80 meter, full-wave loop. I feed the loop antenna 
> with 50 ohm coax and use a 2.5 to 1 matching ballun at the feedpoint 
> of the antenna. The loop works extremely well on all bands 80 through
> 10 meters, including the WARP bands. However, there is a sizable 
> mismatch on some bands at the feedpoint of the antenna. Without an 
> antenna tuner, this mismatch would present such a high SWR at the 
> output of the transceiver or amplifier that the protection circuits 
> would reduce the power to zero or, in the case of the amp, it would 
> kick it off. The mismatch is so high that the internal tuner of the
> TS-590 cannot handle it. So, I use a LDG AT1000PRO II external, 
> automatic antenna tuner, which has a much wider matching range, and it 
> can handle the mismatch and the power of the ALS-600 just fine.
> However, even though I am able to get my SWR down to 1.0 to 1 on some 
> bands and 1.5 to 1 or better on the others, I cannot run the amp at 
> full power because if I do, the reflected power is so high, over 50 
> watts, that it causes my ALS-600 to kick off. Therefore, I am forced 
> to
reduce my output power down to the point where the reflected power is low
enough that it won't shut the amp down.
> Consequently, instead of putting out 600 watts from the amp, I have to 
> reduce the power to where I am putting out only about 300 watts. This 
> keeps my reflected power level below 50 watts, which is the critical 
> level for the
> ALS-600 amp, keeping it from completely shutting down.
>
>   
>
> Many years ago, when I was a young, foolish teenager, I put up an 
> antenna that had such a high SWR that I could get RF burns from the 
> Microphone of my transmitter. The transmitter was a Heathkit DX-40, 
> which had a PI-output circuit that would allow me to load-up about 
> anything for an antenna, but back in those days, there were no 
> protection circuits to automatically shut the rig down if the SWR or 
> reflected power was excessive. As a result, the high SWR and reflected 
> power from trying to load and extremely mismatched antenna caused my 
> tank coil to get so hot that it melted the plastic insulators that 
> separated the windings of the tank coil; this caused the tank coil to 
> short, which, in turn, created a chain reaction, ending up in wiping 
> out the entire power supply. My point is to simply illustrate what 
> high SWR and reflected power could do to your transceiver or amp if it
weren't for the protection circuits that are built into the modern gear.
> However, even with the protection circuits, it is important to strive 
> to achieve the best possible resonant frequency match with your 
> antenna and then, between the feedline and your antenna and again 
> between the feedline and the output of your equipment.
>
>   
>
> I've had three people write to me off list asking me questions that 
> related to this whole topic, and so, I thought I would simply write 
> this up and post it to the list. I'm not trying to show-off what I 
> know; rather, I might be showing-off what I don't know because there 
> is a lot more about this stuff that I know very little about, and I am 
> absolutely certain that many of you know tons more about some of this 
> stuff than I do. I'm just trying to be helpful to some of the people 
> that might be new that do not understand some of these things.
>
>   
>
>    
>
>   
>
>   
>
>   
>
> Dr. Ronald E. Milliman
>
> Retired Professor of Marketing
>
>   
>
> President: Millitronics, Inc. (millitronics.biz)
>
> President: South Central Kentucky Council of the Blind (SCKCB.ORG)
>
>   
>
>